<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"> 
<title>CSS基本语法</title> 
<style>
p.margin2{
    margin:2px 2px 2px 2px
}
p.margin20{
    margin:20px 20px 20px 20px
}
</style>
</head>

<body>
    <p class="margin2">这是margin=2px</p>
    <p class="margin2">这是margin=2px</p>    
    <p class="margin20">这是margin=20px</p>
    <p class="margin20">这是margin=20px</p>
</body>
</html>